1. Field of the Invention
The present invention relates to a wiring board on which bumps are formed and a method for manufacturing the same, and also relates to a semiconductor device using the wiring board.
2. Description of Related Art
Conventionally, a method for manufacturing a semiconductor device has been known in which a semiconductor element is face-down mounted on a wiring board provided with bumps and then electrode pads on the semiconductor element are bonded to the bumps on the wiring board using a TAB (Tape Automated Bonding) method commonly used for the manufacture of semiconductor devices for liquid crystal etc. (see JP 2003-243455 A, for example).
Hereinafter, a conventional wiring board provided with bumps, a semiconductor device using such a wiring board, and a method for manufacturing such a semiconductor device will be described with reference to the drawings. FIG. 12 is a plan view showing a conventional wiring board 1, and FIG. 13 is a sectional view taken along the line A-A′ in FIG. 12.
In FIGS. 12 and 13, reference numeral 2 denotes an insulating base, and reference numeral 3a denotes conductor wirings formed on a surface of the insulating base 2. A bump 4 is formed on a leading end portion of each conductor wiring 3a. In regions on both sides of the conductor wirings 3a, dummy conductor wirings 3b, each having the same structure as the conductor wiring 3a, are provided. The bumps 4 are not formed on the dummy conductor wirings 3b. A protective film 5 for protecting the conductor wirings 3a has an opening provided at a region around the bumps 4, thereby exposing the bumps 4. At both end portions of the insulating base 2, the protective film 5 covers the dummy conductor wirings 3b. Furthermore, second conductor wirings 6 are formed along respective side edges of the insulating base 2. The second conductor wirings 6 are used to supply electricity to the conductor wirings 3a when forming the bumps 4 by electroplating.
FIG. 14 is a sectional view showing a semiconductor device obtained by face-down mounting a semiconductor element 7 on the conventional wiring board 1. Electrode pads 7a are formed on the semiconductor element 7 (on the lower surface in FIG. 14), and the electrode pads 7a are bonded to the bumps 4 of the wiring board 1.
In the wiring board to be used for packaging according to the TAB method, the insulating base etc. are formed of a flexible material or formed so as to have flexibility, and the steps of supplying the wiring board, mounting the semiconductor element on the wiring board, carrying out inspection after the semiconductor element has been mounted, etc. are performed continuously by a reel-to-reel method. In order to impart flexibility to the wiring board, a flexible tape formed of PI (Polyimide) or the like and having a thickness of about 40 μm is used as the insulating base 2. The conductor wirings 3a on the insulating base 2 are formed by patterning an about 8 μm thick Cu foil through etching. The bumps 4 are formed on the respective conductor wirings 3a so as to have a thickness of about 10 μm by copper electroplating. The protective film 5 is formed by printing an about 10 μm thick epoxy resin or PI resin in a desired pattern and then curing the resin. The surfaces of the conductor wirings 3a and the bumps 4 are plated with Au, Sn, or the like for bonding and protection against corrosion.
FIG. 15 is a side view schematically showing an apparatus used for mounting the semiconductor element 7 on the conventional wiring board 1 by the TAB method. In FIG. 15, the wiring board 1 and the semiconductor element 7 are the same as those shown in FIGS. 12 to 14. The wiring board 1 is wound around a first reel 9 to form a winding body in which the wiring board 1 and a first protective tape 8 are layered alternatively. The wiring board 1 is supplied in the arrow direction by unwinding the winding body. The first protective tape 8 serves to protect the conductor wirings 3a and the bumps 4. The first protective tape 8 that is unwound from the first reel 9 when supplying the wiring board 1 is wound up and held by a second reel 10.
The wiring board 1 supplied passes between a mounting head 11 and a mounting stage 12. The rear surface of the semiconductor element 7 is attached to the head 11 so that the principal plane of the semiconductor element 7 faces the surface of the wiring board 1. In this state, the semiconductor element 7 and the wiring board 1 are pressed against each other while applying pressure and heat thereto. Thus, the bumps 4 on the wiring board 1 and the electrode pads 7a on the semiconductor element 7 are bonded to each other, whereby the semiconductor element 7 is face-down mounted on the wiring board 1.
A second protective tape 13 is supplied from a third reel 14 and is used to protect the wiring board 1 on which the semiconductor element 7 has been face-down mounted. The wiring board 1 on which the semiconductor element 7 has been mounted is wound up by a fourth reel 15 with the second protective tape 13 being placed on the wiring board 1 and is held by the fourth reel 15 in the state where the wiring board 1 and the second protective tape 13 are layered alternatively. Reference numeral 16 denotes feed rollers for feeding the wiring board 1. Note here that arrows shown in FIG. 15 indicate the directions in which the wiring board 1 and the first and second protective tapes 8 and 13 are moved and the direction in which the first, second, third, and fourth reels 9, 10, 14, and 15 are rotated.
FIG. 16 is a perspective view schematically showing the wiring board-winding body 9A wound around the first reel 9 for supplying the wiring board 1, which is shown in FIG. 15. FIG. 16 shows the state where the wiring board 1 and the first protective tape 8 are wound around the first reel 9 such that the wiring board 1 and the first protective tape 8 are layered alternately.
FIG. 17 is a side view showing a portion of the winding body shown in FIG. 16, in which the wiring board 1 and the first protective tape 8 are layered alternately, and FIG. 18 is a sectional view taken along the line B-B′ in FIG. 16.
In FIGS. 17 and 18, reference numeral 17 denotes embossed portions formed along the edges of respective end portions of the first protective tape 8. By the embossed portions 17, a space is formed between the bumps 4 and the first protective tape 8. Accordingly, the first protective tape 8 does not contact the bumps 4, so that the bumps 4 can be prevented from being damaged or contaminated due to contact with the first protective tape 8. Therefore, it is possible to prevent the occurrence of poor bonding between the electrode pads 7a and the bumps 4 when mounting the semiconductor element 7 on the wiring board 1.
Since the first protective tape 8 needs to have flexibility and mechanical strength, a tape formed of a material such as PEI (Polyetherimide), PET (Polyester), or PI and having a thickness of 125 μm to 250 μm is used as the first protective tape 8.
The embossed portions 17 of the first protective tape 8 generally are formed by secondary processing the end portions of the first protective tape 8 as shown in FIG. 17 with the use of a die. The embossed portions 17 are formed with a pitch of 5 mm to 15 mm so as to have a height of 1 mm to 3 mm, considering the thickness of the first protective tape 8, the amount of plastic deformation at the time of the processing with the die, and the return amount from the plastic deformation after the processing with the die, and the strength of the embossed portions.
As an alternative method of obtaining the same effect as that produced by the embossed portions 17 of the first protective tape 8, a method has been used in which, as shown in FIGS. 19 and 20, openings 18 are provided in respective end portions of the first protective tape 8 and spacers 19, which are protrusions, are inserted into the openings.
Considering the deterioration in strength of the first protective tape 8 caused by the formation of the openings 18 and the mechanical strength of the spacers 19, the spacers 19 are formed with a pitch of about 10 mm so as to have a height of about 3 mm. As a material of the spacers 19, LCP (Liquid Crystal Polymer) or the like is used in view of its mechanical strength, ease of processing, etc.
According to the above-described conventional manufacturing method, it is necessary to provide the embossed portions 17 or the spacers 19 along the edges of the respective end portions of the first protective tape 8 in order to prevent the bumps 4 from being damaged or contaminated by the contact with the first protective tape 8 when winding the wiring board 1 and the first protective tape 8 around the first reel 9 such that the wiring board 1 and the first protective tape 8 are layered alternately.
However, as described above, the embossed portions 17 and the spacers 19 formed on the first protective tape 8 have a height of 1 mm to 3 mm, which is large relative to the thickness 40 μm of the wiring board 1. Thus, when the wiring board 1 and the first protective tape 8 are wound around the first reel 9 such that the wiring board 1 and the first protective tape 8 are layered alternately, the first reel 9 can hold only a short length of the wiring board 1. This poses a problem in that the frequency of replacing the first reel 9 that supplies the wiring board 1 in the manufacturing process according to the TAB increases, resulting in decreased productivity.
Moreover, the secondary processing for providing the embossed portions 17 or the spacers 19 in the respective end portions of the first protective tape 8 increases the cost required for processing the first protective tape 8.